The operation speed of Metal-Oxide-Semiconductor (MOS) transistors is substantially related to the drive currents of the MOS transistors, and the drive currents are further related to the mobility of charges. For example, NMOS transistors have high drive currents when the electron mobility in their channel regions is high, while PMOS transistors have high drive currents when the hole mobility in their channel regions is high.
Compound semiconductor materials of group III and group V elements (referred to as compound semiconductors hereinafter) are good candidates for forming transistors due to their high electron mobility. Therefore, III-V based transistors have been explored. III-V compound semiconductor films, however, need to be grown on other substrates because it is difficult to obtain bulk III-V crystals. The formation of III-V compound semiconductors typically includes an epitaxy growth, followed by a chemical mechanical polishing (CMP) to remove excess III-V compound semiconductors. CMP is commonly used in the semiconductor manufacturing industry to polish and remove materials from a surface of a semiconductor substrate. The performances of the CMP, such as the removal rate and the selectivity, are closely related to the content of the slurry applied in the CMP.